Currently linear media delivery, such as of live television channels, is delivered over IP networks uses one of two quite different networking technologies: one based on multicast and the other based on unicast. With multicast transmission, a single multicast stream carrying the content is pushed from a content server to multiple network nodes simultaneously, with those network nodes duplicating the content and forwarding to any subsequent nodes or clients as required. With unicast transmission, multiple streams of content are pulled from the server, one stream for each device consuming the content, typically using HTTP over TCP.
Multicast makes efficient use of the network when delivering the same content at the same time to many end devices. However, it often requires continual allocation of network resources regardless of the amount of viewing, so that channel is delivered through the network even if no-one is actually watching it. In addition, not all end devices, such as some tablets and smartphones, presently support multicast.
Unicast suffers from sending multiple copies of the same channel content through the network, but requires no usage-independent allocation of network resources. However, if audiences are expected to be small for a particular channel, it may be more efficient overall to deliver that channel over unicast instead. This means that for those parts of the network where a channel has no viewers, the channel is not delivered and the network capacity can be re-used. Unicast is also capable of delivering to all end devices.
The choice of unicast or multicast delivery for one or more channels is usually a basic architectural decision made early on in planning and difficult to change. However, it would be beneficial to be able to switch between multicast and unicast depending on viewing numbers for example, in order to utilise network resources as efficiently as possible.
US patent application 2013/0024582 describes a system and method for dynamically switching between unicast and multicast delivery of media content in response to changes in concurrent demand for access to the media content.
European patent application EP2767060 describes a system that encapsulates unicast traffic for tunnelling over multicast. Mark-ups are inserted into the multicast stream which can be used to de-encapsulate the traffic and re-create the unicast stream.
European patent application EP2586170 describes a general multicast to unicast conversion system, but does not address synchronisation or segmentation issues.